Pathological anatomies such as tumors and lesions can be treated with an invasive procedure, such as surgery, which can be harmful and full of risks for the patient. A non-invasive method to treat a pathological anatomy (e.g., tumor, lesion, vascular malformation, nerve disorder, etc.) is external beam radiation therapy, which typically uses a therapeutic radiation source, such as a linear accelerator (LINAC), to generate radiation beams, such as x-rays. In one type of external beam radiation therapy, a therapeutic radiation source directs a sequence of x-ray beams at a tumor site from multiple co-planar angles, with the patient positioned so the tumor is at the center of rotation (isocenter) of the beam. As the angle of the therapeutic radiation source changes, every beam passes through the tumor site, but passes through a different area of healthy tissue on its way to and from the tumor. As a result, the cumulative radiation dose at the tumor is high and that to healthy tissue is relatively low.
The term “radiosurgery” refers to a procedure in which radiation is applied to a target region at doses sufficient to necrotize a pathology in fewer treatment sessions or fractions than with delivery of lower doses per fraction in a larger number of fractions. Radiosurgery is typically characterized, as distinguished from radiotherapy, by relatively high radiation doses per fraction (e.g., 500-2000 centiGray), extended treatment times per fraction (e.g., 30-60 minutes per treatment), and hypo-fractionation (e.g., one to five fractions or treatment days). Radiotherapy is typically characterized by a low dose per fraction (e.g., 100-200 centiGray), shorter fraction times (e.g., 10 to 30 minutes per treatment) and hyper-fractionation (e.g., 30 to 45 fractions). For convenience, the term “radiation treatment” is used herein to mean radiosurgery and/or radiotherapy unless otherwise noted.
Image-guided radiation therapy (IGRT) systems include gantry-based systems and robotic arm-based systems. In gantry-based systems, a gantry rotates the therapeutic radiation source around an axis passing through the isocenter. Gantry-based systems include C-arm gantries, in which the therapeutic radiation source is mounted, in a cantilever-like manner, over and rotates about the axis passing through the isocenter. Gantry-based systems further include ring gantries having generally toroidal shapes in which the patient's body extends through a bore of the ring/toroid, and the therapeutic radiation source is mounted on the perimeter of the ring and rotates about the axis passing through the isocenter. Traditional gantry systems (ring or C-arm) deliver therapeutic radiation in single plane (i.e., co-planar) defined by the rotational trajectory of the radiation source. Examples of C-arm systems are manufactured by Siemens of Germany and Varian Medical Systems of California. In robotic arm-based systems, the therapeutic radiation source is mounted on an articulated robotic arm that extends over and around the patient, the robotic arm being configured to provide at least five degrees of freedom. Robotic arm-based systems provide the capability to deliver therapeutic radiation from multiple out-of-plane directions, i.e., are capable of non-coplanar delivery. Accuray Incorporated of California manufactures a system with a radiation source mounted on a robotic arm for non-coplanar delivery of radiation beams.
Associated with each radiation therapy system is an imaging system to provide in-treatment images that are used to set up and, in some examples, guide the radiation delivery procedure and track in-treatment target motion. Portal imaging systems place a detector opposite the therapeutic source itself to image the patient for setup and in-treatment images, while other approaches utilize distinct, independent image radiation source(s) and detector(s) for the patient set-up and in-treatment images. Target or target volume tracking during treatment is accomplished by comparing in-treatment images to pre-treatment image information. Pre-treatment image information may comprise, for example, computed tomography (CT) data, cone-beam CT data, magnetic resonance imaging (MRI) data, positron emission tomography (PET) data or 3D rotational angiography (3DRA) data, and any information obtained from these imaging modalities (for example and without limitation digitally reconstructed radiographs or DRRs).
In one common scenario, the therapeutic source is a linear accelerator (LINAC) producing therapeutic radiation (which can be termed an “MV source”) and the imaging system comprises one or more independent x-ray imaging sources producing relatively low intensity, lower energy imaging radiation (each of which can be termed a “kV source”). In-treatment images can comprise one or more (preferably two) two-dimensional images (typically x-ray) acquired at one or more different points of view (e.g., stereoscopic x-ray images), and are compared with two-dimensional DRRs derived from the three dimensional pre-treatment image information. A DRR is a synthetic x-ray image generated by casting rays through the 3D imaging data, where the rays simulate the geometry of the in-treatment x-ray imaging system. The resulting DRR then has approximately the same scale and point of view as the in-treatment x-ray imaging system, and can be compared with the in-treatment x-ray images to determine the position and orientation of the target, which is then used to guide delivery of radiation to the target.
There are two general goals in radiation therapy: (i) to deliver a highly conformal dose distribution to the target volume; and (ii) to deliver treatment beams with high accuracy throughout every treatment fraction. A third goal is to accomplish the two general goals in as little time per fraction as possible. Delivering a conformal dose distribution requires, for example, the ability to deliver non-coplanar beams. Delivering treatment beams accurately requires the ability to track the location of the target volume. The ability to increase delivery speed requires the ability to accurately and precisely move the radiation source without hitting other objects in the room or the patient.
One or more issues arise with respect to known radiation therapy systems that are at least partially addressed by one or more of the preferred embodiments described further hereinbelow. Generally speaking, these issues relate to less than optimal trade-offs and compromises in both functionality and patient experience presented by and among known robot arm-based systems and gantry-based systems. By way of example, the rotational trajectories of known ring gantry-based systems tend to provide for good mechanical stability and relatively high mechanical drive speeds, but tend to be less versatile in the kinds of therapy plans that can be provided, such as an inability to provide apex-oriented radiation beams for cranial treatments and non-coplanar radiation treatment delivery. On the other hand, known robot arm-based systems tend to provide high versatility and a wide range of radiation treatment profiles, including apex-oriented radiation beams for cranial treatments and non-coplanar radiation treatment delivery, but tend to require longer times per treatment fraction due to the limited speeds at which the robot arm can manipulate the radiation treatment head. Other issues arise as would be apparent to a person skilled in the art in view of the present teachings.